A contemporary wireless communication system for repeating wireless signals, such as distributed antenna system 10, is shown in FIG. 1, and includes a number of remote units 12 distributed to provide coverage within a service area of the system 10. In particular, each remote antenna unit 12 typically includes an antenna 14 and suitable electronics. Each remote unit is coupled to a master unit 16 with a suitable media, such as a coaxial cable or optical fiber. Each master unit 16 is, in turn, coupled to an RF combination network 18 that combines the signals from one or more (1-N) base transceiver stations (“BTS,” or more simply, “base station”) 20 (hereinafter, “BTS” 20). As illustrated in FIG. 1, the system 10 may include a plurality of master units 16 and may couple to a plurality of BTSs 20, each master unit 16 configured to provide a combination of the signals from the BTSs 20 to the various remote units 12. The link 21 between the BTSs 20 and the RF combination network 18 and various master units 16 may be a wired or wireless link.
In FIG. 1, each remote unit 12 broadcasts a wireless signal 24 that, in turn, is transceived with a wireless device 26 that may be a mobile device, such as a telephone device or a computing device. In particular, and as discussed above, the wireless signal 24 from each remote unit 12 may be a combination of signals from the BTSs 20. Thus, the wireless device 26 may communicate with the system 10 through any of the wireless signals 24 from the remote units 12. Specific embodiments of the system 10 illustrated in FIG. 1 may include ION-B systems and ION-M systems, both of which are distributed by Andrew LLC, a division of CommScope, Inc., of Hickory, N.C.
To improve wireless communications, such as communications from a base station to mobile devices, Multiple-Input/Multiple-Output (“MIMO”) technology might be utilized to provide advanced solutions for performance enhancement and broadband wireless communication systems. Substantial improvements may be realized utilizing MIMO techniques with respect to the traditional SISO systems. MIMO systems have capabilities that allow them to fully exploit the multi-path richness of a wireless channel. This is in contrast with traditional techniques that try to counteract multi-path effects rather than embrace them. MIMO systems generally rely upon multi-element antennas at both of the ends of the communication links, such as in the base station and also in the wireless device. In addition to desirable beam-forming and diversity characteristics, MIMO systems also may provide spatial multiplexing gain, which allows multi data streams to be transmitted over spatially-independent parallel sub-channels. This may lead to a significant increase in the system capacity without extending the bandwidth requirements. Generally, a SISO system, such as that illustrated in FIG. 1, cannot increase spectral efficiency by taking advantage of spatial MIMO technology.
For example, the wireless device 26 of FIG. 1 receives one signal communication signal only, though it may be in the range of a plurality of remote units 12. The wireless signals 24 from each remote unit are typically at the same frequency and carry the same data, and communication between a plurality of remote units 12 and the wireless device 26 simultaneously may result in signal degradation and collisions. In a best case scenario, the multipath nature of the communication channel can be turned into an advantage by sophisticated equalizer algorithms. However, data bandwidth from the wireless device 26 is constricted to the speed of reception and processing of data from one remote unit 12.
It is therefore, desirable to take advantage of spatial MIMO signals within a distributed antenna system.